Let’s back up for a minute.
Each month your ovaries release an egg about 14 days before the first day of your period. This is called ovulation. When you and your partner have unprotected sex around the time of ovulation, his sperm swim to meet your egg.
When the egg and sperm meet, it’s called fertilization. The fertilized egg (also called an embryo) moves through your fallopian tubes and attaches to the wall of your uterus where it grows and develops into a baby. When the embryo attaches to the uterus, it’s called implantation.
You can get pregnant if you have unprotected sex any time from 5 days before and the day of ovulation.
What if you have sex during your period?
It’s possible for women with a very short menstrual cycle or a very long period to become pregnant by having sex during their period. Many women have cycles that are 28 days or longer. (Your cycle length is measured from the first day of your period and all the days after, until your next period.) But others have shorter cycles, or longer periods, so ovulation can happen right after your period ends. Since sperm can live in your reproductive tract for up to 5 days before ovulation, it’s possible that you could have sex during your period and conceive when you ovulate days later.
If you’re not ready to get pregnant, use birth control until you’re ready. Talk to your health care provider about the right birth control for you.